1. Field of the Invention
The present invention relates to an optical recording apparatus such as a laser printer for making an optical recording by using a semiconductor laser having a blue color wavelength (referred to as “blue color semiconductor laser” hereinafter).
2. Description of the Related Art
In the high-speed laser printer as a typical example of the optical recording apparatus, because the photosensitive material having the enough endurance must be employed, the selenium photosensitive drum that has a small sensitivity to a red color but is highly sensitive to a blue color, or the like is employed. Therefore, in the high-speed laser printer in the prior art, the optical system to which the argon laser to output a laser beam of a blue color wavelength of 488 nm is applied was employed.
A schematic view of an example of an optical system to which an argon laser 101 is applied is shown in FIG. 2. In this optical system, a laser beam emitted from the argon laser 101 is divided into multiple beams (five beams in FIG. 2) by a diffraction grating 102 to pass through a lens 103, then the beams are modulated by a multichannel acousto-optic modulator 104, and then irradiated onto a lens 105. The lens 103 and the lens 105 are provided to expand a beam diameter. In addition, the multiple beams passed through the lens 105 are reflected by reflecting mirror 106 to pass through a Dove prism 107, which adjusts a slant scanning angle of the multiple beams, and a cylindrical lens 108, which focuses the beam onto a rotating polygon mirror 110 in the paper feed direction, then are deflected collectively by the rotating polygon mirror 110, and then are irradiated onto a photosensitive drum 111 via scanning lenses 109. This process makes it possible to scan collectively the laser beam consisting of the multiple beams and to thus execute the printing at a high speed.